When a child says runned, something has gone right
Small children usually say ran before they say runned. They have heard ran, stored it whole and repeated it. Then one day they work out the rule — add -ed for things that already happened — and immediately apply it to everything, including all the words that do not follow it.
So the correct version disappears and is replaced by runned, swimmed, throwed and drawed, sometimes for a year or more. It looks like going backwards and it is the opposite: the child has stopped copying and started reasoning. RUN, SWIM, THROW, DRAW and CATCH are all irregular, and all five will be mangled before they settle down.
English-speaking toddlers load up on nouns early — cup, dog, shoe — and pick up verbs more slowly. This was assumed to be simply how language works, until researchers compared them with children learning Korean and Mandarin, who take on verbs much earlier.
The grammar explains it. Those languages let a speaker drop the obvious noun and end the sentence on the verb, which is the position a small child hears most clearly. An English toddler hears the verb buried in the middle of the sentence. The order is a property of the language, not of the child.
Skipping is the hard one
The words in this grid are not equally difficult, and the difficulty has nothing to do with spelling. CRAWL, WALK, RUN and JUMP arrive on their own. HOP needs balance on one leg and turns up around three or four.
SKIP is last, usually somewhere around five or six, because it is two different movements alternating between two legs and the brain has to keep them out of step. Plenty of five-year-olds can read the word long before they can do it. Throwing and catching follow their own slow schedule too — CATCH with two hands and a stiff body comes well before anything that looks like fielding.
Do it and you will remember it
Memory researchers have tested this repeatedly: people who physically perform an action while learning its name recall it far better later than people who only read or hear it. The effect is strong, it is easy to reproduce, and it is more pronounced in young children than in adults.
Which makes this particular puzzle unusually easy to turn into something else. Find WAVE and wave. Find CLAP and clap twice. Find JUMP and there is no sensible way to stop what happens next. A quiet activity and a loud one, in the same ten minutes.
Twenty things to go and do
The grid divides neatly. Ways of travelling: RUN, WALK, JUMP, HOP, SKIP, CLIMB, CRAWL, SWIM and DANCE. Things done with the hands: CLAP, THROW, CATCH, KICK, DRAW and WAVE. And the quieter ones: SIT, STAND, READ, SING and PLAY.
Two of them stand apart. CRAWL and WALK are the only entries on the list that a child arrives at without anybody teaching them, usually to the alarm of whoever is nearest. READ and DRAW sit at the far end of the scale — nobody in history has done either of those by accident.